Ultra high frequency antenna system



Sept. 4, 1951 E. D. MCARTHUR ULTRA HIGH FREQUENCY ANTENNA SYSTEM Filed Dec. 51, 1948 Fig. I.

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Inventor: Elmer- D. MoArthur',

His Attorney,

Patented Sept. 4, 1951 ULTRA HIGH .FREQUENCY ANTENNA "SYSTEM'-' .Elmer D. McArthur, Schenectady, n assignpr to General Electric Company, a cdrporationpil Newiork Application'December s1, 1948,'Serial:No..68,-6iL7 My invention relates to antenna systems for radiation of ultra-high frequency electromagnetic waves, and more particularly to antenna systems employing parabolic reflectors for the directive propagation :of ultra-high-frequency radiation.

An object of my invention is to providea new .and improveddeyicefor illuminatinga parabolic reflector which is of simple construction ,and

eas l unted onathe en o a W veg i An additional object is to provide an lilluminating device for an antenna system of the above type which reduces undesirable reflections from the wave guide across the face of a parabolic reflector.

In general, my invention comprises a conductive horn closed at its narrower end and facing a parabolic reflector substantially at the focal point thereof. The horn is fed by a wave guide extending through the center of the reflector and aimed at the closed end of the horn. A septum secured to opposing sides of the open end of the guide functions to support the horn in its proper position.

For a more complete understanding of my invention, reference should be made tothe accompanying drawing in which Fig. l is a sectional view of an illuminating device constructed in accordance with my invention; Fig. 2 is a perspective view illustrating a method of mountin the illuminating device of Fig. 1 on an end oi a wave guide; Fig. 3 is a sectional view illustrating the use of the illuminating device of Fig. l in conjunction with an antenna system employing a parabolic reflector; and Fig. 4 is a sectional view of an antenna system similar to Fig. 3, but incorporating a modification of my invention whereby variations in the radiation pattern may be obtained.

Referring to Fig. l, I have shown my invention in one form as applying to a rectangular wave guide I which represents an output guide from an ultra-high frequency transmitting system. A flared horn-shaped conductive member 2 is mounted on the end of Wave guide I by a flat plate or septum 3 inserted within wave guide I along the longitudinal axis thereof and parallel to the pair of opposing walls of the wave guide which happen to be of greater dimensions. The septum 3 is secured to the other pair of opposing interior walls by any suitable means such as welding. One end of septum 3 extends beyond the open termination of wave guide I and is secured to a conductive transverse central wall 4 of member 2. The sides of member 2 extend 2 Claims. (01. engages) I an u a lv .b e t m wal eve t e .d :o wave gui e @I to or. 1 ms e tio whi h a e we gna a q c flect I s i lust ated in I. @5 W ve g id e end throughthe centerof'reflector 6 and istermin 'nverted hornof -.rectang'ular nated susbtantially the {focal point thereof. Th il uminatin vi ed scribe at 0 ..i; sine wav gu de I .c n uct v i embe d septum 3.11s pa ti u arl a apt d 9 11. with a r t ngula er sa d? e ectri .mo o ave zg epa at th order denoted as a TEm wave. In a wave of this type, no field components vary in the vertical or y direction, and the only electrical field component is the one passing between the top and bottom of the guide. The corresponding charges induced by the varying electrical field range from zero along the side walls of wave guide I to maximum at the center of the top and bottom conductive walls. The magnetic field, forming closed paths around the electrical displacement currents arising from the electrical field, causes I both a longitudinal current flowing along the top and bottom of the guide and a current from top to bottom around the periphery of the guide.

The septum 3, therefore, in this mode of operation, doe not substantially affect the wave propagation through the guide since it is connected between points of zero electrical charge and through an area of the guide where there is no concentration of magnetic flux. As illustrated by the electrical vectors A of Fig. 1, the direction of the electrical field is not afiected by its passage through the septum 3. The total wave is reversed by conductive member 2 without changing the phase relation of the radiation pattern on either side of the septum 3. The parabolic reflector 6 receives the total wave in the same manner as if it had been directly i1- luminated by a completely open horn facing the reflector.

Referring now to Fig. 4, I have shown a modification of my invention whereby a variation in the focal angle of illumination can be obtained. An angular conductive collar or flange 7 surrounds the open end of wave guide I and extends back over the guide. The sides 5 of conductive member 2 are flared at a greater angle than in Fig. 1 thereby maintaining the relative dimension, d, of the mouth of the horn in order to properly match the impedance of the radiating device to that of free space. The greater flare angle results in a variation of the radiation pattern produced by the antenna system. Many different patterns of radiation can, of course, be

obtained by varying either the flare angle or the dimensions of conductive member 2.

While I have shown a particular embodiment of my invention, it is to be understood that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is: r

1. In an antenna system of the type employing a parabolic reflector, means for illuminating said reflector comprising a rectangular wave guide extending through the center oi. said refiector and having an open end substantially at the focal point thereof, a conductive horn-shaped member having a transverse central wall facing -principal dimensions, said plate extending and secured within said guide to the other pair of walls thereof.

ELMER D. McARTI-IUR.

REFERENCES CITED The following references are of record in the file of this patent:

said open end and having angular sides extenda. rectangular wave guide extending through said reflector and having an open end substantially at the focal point thereof, a conductive collar secured to and surrounding the open end V UNITED STATES PATENTS Number Name Date 2,422,184 Cutler June 17, 1947 2,455,286 Werner Nov; '30, 1948 2,505,424 Moseley Apr. 25, 1950 OTHER REFERENCES Principles of Radar, MIT,Radar School Staif, 2nd edition, McGraw-Hill Book Co., 1946, chapter 9, page 88.

Radar System Engineering, Ridenour, Mc- Graw-Hill, June 23, 1947, page 274.

Proc. IRE, vol., 35, page 1284 to 1294, November 1947. v 

